Thermal transport in novel carbon allotropes with sp2 or sp3 hybridization: An ab initio study

Thermal transport in most carbon allotropes is determined by phonons. The properties of the atomic bonds will influence the phonon transport process directly. In this paper we studied two novel carbon allotropes as examples, one novel allotrope phase is topological semimetal in an sp2 bonding network with a 16-atom body-centered orthorhombic unit cell (BCO-C16) [Phys. Rev. Lett. 116, 195501 (2016)PRLTAO0031-900710.1103/PhysRevLett.116.195501] and the other novel allotrope is derived by substituting each atom in diamond with a carbon tetrahedron (T-carbon) [Phys. Rev. Lett. 106, 155703 (2011)PRLTAO0031-900710.1103/PhysRevLett.106.155703], which possesses an sp3 bonding network. Graphene and diamond with standard sp2 and sp3 hybridization, respectively, are also examined for comparison. We explored the related properties of the atomic bonds of these allotropes with the density functional theory, i.e., the atomic orbital hybridization, effective spring constants of atomic bonds, the anharmonicity of atomic bonds, etc. By comparing the results, we unveiled the veil behind different lattice thermal conductivities of these allotropes at atomic bond levels (BCO-C16 vs graphene and T-carbon vs diamond), despite their similar hybridization. In addition, within the framework of a phonon Boltzmann transport equation, the mode level phonon transport properties of the four carbon allotropes are also studied in detail, which are well consistent with the information from atomic bonds. We expect that the method of analyzing the strength and anharmonicity of atomic bonds here will be helpful for studying the thermal transport in crystalline materials in the future.